The present invention relates to a multilayer tube for guiding fuel fluid or brake fluid, comprising an outer protection layer, a barrier layer radially within the outer protection layer, an intermediate layer radially within the barrier layer, and an inner layer radially within the intermediate layer, wherein at least two of the layers are co-extruded layers.
Further, the present invention relates to a method of manufacturing a multi-layer tube, particularly a multilayer tube as mentioned above.
Multilayer tubes for guiding fuel fluid or brake fluid are used at large scale in automobile applications, e.g. for guiding fuel fluid from a tank to an injection system of an internal combustion engine. In addition, other fluids can be guided through such multilayer tubes, including lubrication fluids, brake fluids etc., wherein the internal pressure within the multilayer tube is preferably below 2 bar.
Multilayer tubes include multiple layers which address certain needs in such tubes.
For example, an outer protection layer is typically provided in order to protect the inner layers again harsh environments, as for example within an engine compartment of a motor vehicle. In these environments, both mechanical and heat stress can occur, but also the exposure to fluids like water, oil, etc. that should not intermix with the fluid that is guided within the multilayer tube.
On the other hand, the inner layer comes into contact with the fluid to be guided. In case that the fluid is for example a fuel fluid that contains alcohol or similar substances, it must be ensured that the inner layer has a high wash-out resistance.
The intermediate layer, typically, provides a certain rigidity and stability of the tube.
Finally, the barrier layer has the task to provide a barrier between the inside of the multilayer tube and the outside of the multilayer tube, for example a good barrier ability with regard to ethanol fuel, e.g. CE10.
In the prior art, it is well known to use EVOH (ethylen vinyl alcohol copolymer) as a base material for the barrier layer. Further, it is known to use polyamide for the outer protection layer and/or for the intermediate layer. In combination, it is known to provide adhesive layers between the polyamide layers and the EVOH barrier layer.
Further, it is known to use, as an inner layer, a low extractable polyamide 6.12 (Plastics Today, “Multilayer fuel tube features inner layer of low extractable PA612: perfect for vehicles powered by fuels that contain alcohol” in K Show, Automotive and Mobility, Extrusion: Pipe & Profile Materials on Aug. 30, 2016).